any confidential mission

Hola. ¿Me podríais decir como se traduce la palabra "mission" en el texto siguiente?: This, and some other letters. I determined to post myself -a love of solitary and surreptitious walks being a peculiarity the country always deveops in me; and accordingly, without asking anyone else in the house if he or she desired to send any confidential mission by the next day´s mail, I started off to the nearest village all alone.
Gracias por la ayuda.